The present invention relates to a pressure regulating valve used for regulating fluid pressure delivered to hydraulic devices such that the fluid pressure is maintained at a preset target value. This invention is applicable particularly, but not exclusively, to a vehicle automatic transmission.
Pressure regulating valves have been used in hydraulic circuits to maintain hydraulic pressure at a constant pressure. Japanese Patent Provisional Publication (Heisei) 5-164223 discloses a pressure regulating valve which is shown in FIG. 2. According to the related art reference, a pressure regulating valve 100 comprises a spool 100b, and as shown by the top half of spool 100b in FIG. 2, under a low pressure condition, spool 100b is at a leftmost position within regulating valve 100 according to FIG. 2. When spool 100b is at this leftmost position, a drain port 100f is closed and therefore fluid is not drained, and also, an input port 100c and an output port 100d are in hydraulic communication and therefore fluid from a passage 111 is supplied to a passage 112. Output port 100d is in hydraulic communication with port 100e via passage 112 and a passage 113, and output pressure thereof is delivered via an orifice 114 to a pressure-receiving face of spool 100b. Accordingly, output pressure causes spool 100b to slide to the right according to FIG. 2 against the force of a spring 100a, and when the pressure becomes higher than is necessary, passage 112 (outport 100d) and passage 111 (input port 100c) are closed off as shown by the bottom half of spool 100b in FIG. 2, output port 100d is brought into hydraulic communication with drain port 100f. Thus, fluid pressure of passage 112 is relieved, and the drop in pressure is fed back to port 100e, resulting in spool 100b being pushed back to the left of FIG. 2 by spring 100a. Input port 100c and output port 100d are then once again in hydraulic communication, after which pressure of passage 112 is increased.
Pressure regulating valve 100 regulates the output pressure of passage 112 by the urging force of spring 100a by repetition of the above explained stroke movement of spool 100b. However, the pressure (fluid pressure) is not constant but instead pulsating, as the pressure is output by a pump. When the pulsation (fluid pressure fluctuation) and a natural frequency of vibration of spool 100a coincide, there are instances of self-induced vibration (resonance) occurring.
In order to suppress such resonance of spool 100b, orifice 114 is disposed in port 100e as shown in FIG. 2. That is, the flow rate of fluid fed back from passage 112 to port 100e is regulated, and resonance of spool 100b is regulated or dampened.
Also, in order to achieve an increased damping effect for pressure regulating valve 100, a pressure chamber 121 which is open to the air and where fluid enters and leaves by sliding motion of spool 100b is formed, and an orifice 124 is disposed as a restricting element in a passage 123 which is in hydraulic communication with pressure chamber 121. That is, by provision of orifice 124 to restrict the flow of fluid which is caused to flow out of and into pressure chamber 121 by the sliding movement of spool 100b, a damping effect is produced as a counter to vibration of spool 100b. 